Ignition timing, also referred to as spark timing, can be an important aspect in the performance of an internal combustion engine. Generally, ignition timing relates to how early or late the spark plug fires in relation to the axial position of the piston within the cylinder.
For instance, when the engine is being operated at high speeds, it is desirable to initiate the combustion process early such that the combustion reaction has adequate time to develop and assert its force upon the piston. Thus, an ignition timing control system delivers a spark to the combustion chamber before the piston reaches a top-dead-center (TDC) position, an occurrence commonly referred to as timing advance. Conversely, if the engine is being operated at relatively low speeds, the control system instructs the spark plug to fire at a point closer to TDC (either slightly before or slightly after). In the case where the spark plug fires slightly after TDC, a timing retard has occurred and allows less time for the combustion process to develop. Manipulation of the ignition timing can be helpful for obtaining optimum performance.
An example of an ignition timing control system for use with a low cost, light duty combustion engine is disclosed in U.S. patent application Ser. No. 10/186,522, which is assigned to the present assignee and is hereby incorporated by reference. That application discloses a control system that generally utilizes an engine speed input signal and independent operating sequences to determine a desired ignition timing and an air-to-fuel ratio for a combustible mixture. There are several independent operating sequences, each one of which is designed to optimally control the engine under certain conditions. By utilizing these operational sequences and an engine speed input signal, the control system is able to improve the engine performance and emissions across a wide array of conditions.